Method of producing an electrophotographic plate



United States Patent- 3,507,693 METHOD OF PRODUCING AN ELECTRO-PHOTOGRAPHIC PLATE Yasuo Ueda, 3-32 Kitano-cho, Ikula-ku, Kobe, HyogoPrefecture, Japan; Akira Takatsu, 3-5-16 Kusatsu-cho, Kusatsu, SigaPrefecture, Japan; and Tatsu Aizawa, 6-34 Kuwagu-cho,Higashisumiyoshi-ku, Osaka, Japan No Drawing. Filed Nov. 13, 1967, Ser.No. 682,509

Int. Cl. Hf US. Cl. 117201 7 Claims ABSTRACT OF THE DISCLOSURE Anelectrophotographic printing plate including the base of art paper orthe like coated with a mixture of citric acid and photoconductivemicrocrystalline zinc oxide with water and in some cases with ethylalcohol producing an electrophotographic plate without requiring the useof resins and organic solvents which may be dangerous, theelectrophotographic plate being usable with or without charging theplate.

The present invention relates to electrostatic printing and to the plateand the method of producing the electrophotographic plate. Moreparticularly the invention relates to a composition of matter includinga photoconductive material which will adhere to an electrophotographicplate base of art paper or other suitable base material and which can beproduced economically without employing a resin binder.

Heretofore the methods of producing electrophotographic plates hasincluded mixing a photoconductive material with electrically-insulatingplate forming vehicle with a volatile organic solvent, for example bymixing zinc oxide and a silicone resin with toluene thereby producing aform of photoconductive medium that has already been developed by R.C.A.of America. The silicone resin binder is used for keeping aphotoconductive coating layer adhesively secured to a base plate and forholding electrons emitted by corona discharge. The use of a volatileorganic solvent for the vehicle, however, has several disadvantagesparticularly that the solvent is expensive and therefore uneconomicaland also most organic solvents are inflammable and poisonous therebypresenting a health hazard to factory personnel. Even if water is usedas the vehicle a resin binder is relatively expensive.

Accordingly a principle object of this invention is to overcome theabove described difiiculties and to provide an improvedelectrophotographic plate and a method for producing the plate which iseconomical and can be readily carried out at a minimum of expense.

A further object is to provide a method of producing anelectrophotographic plate without employing a resin binder.

A further object is to provide an electrophotographic plate for use inchargeless electrostatic printing.

Briefly the invention provides a method of making an electrophotographicplate by coating a base plate of suitable material with a mixture of aphotoconductive material, citric acid, and water and then drying thecoating on the base plate. 1

Other and further objects will be apparent as the detailed descriptionproceeds.

"The citric acid and water may be added to the photoconductive materialof microcrystalline zinc oxide or the citric acid may be added to themicrocrystalline zinc oxide dispersed in water or the water may be addedto a mixture comprising the microcrystalline-zinc oxide and citric acid.Also the citric acid may be dissolved in water and added to themicrocrystalline zinc oxide.

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An exothermic reaction takes place between zinc oxide and citric acidand it has been found that the photoconductive coating layer of citricacid and zinc oxide adheres firmly to the base plate as a result of thechemical reaction without the use of a particular binder.

It has also been found that the photoconductive coating layer of zincoxide, citric acid, and water adhere more firmly to the base plate byhaving ethyl alcohol added thereto and using a small amount of water inthe mixture.

The exothermic reaction between citric acid and zinc oxide has theproperty of causing the coating to adhere firmly to the base platewithout requiring the use of an additional binder.

By experiment it has been shown that an electrophotographic plate madeaccording to the present invention can recover from the memory efiect inthree to five minutes after exposure to light. The photographic plate ofthe present invention should be developed within three minutes toproduce a visible image by the usual toner used in electrophotographicreproduction. It has been proved by experiment that theelectrophotographic plate can recover from the memory efiect (theirradiation effect caused by exposing to light) in 3-5 minutes afterexposure, therefore, the electrophotographic plate may be readily usedin making reproductions by the electrostatic printing process. Theelectrophotographic plate of the present invention therefore recoversfrom the memory effect of irradiation to light in three to five minutesand this may be accomplished by placing the electrophotographic plate inthe dark for this period of time. Thereafter, the electrophotographicplate can be exposed to an image pattern of light by any of the usualphotographic means including contact with a negative or projection of animage on the electrophotographic plate and the latent image producedthereby can be developed in the usual manner of electrophotography. Thepresent electrophotographic plate is particularly advantageous in thechargeless electrostatic printing process since the image can be formedwithout requiring the charging of the electrophotographic plate. Thetoner may be charged before coming in contact with the latent imageproduced by the light exposure on the photographic plate and this shouldbe done within three minutes before the electrophotographic plate canrecover from the memory effect.

The electrophotographic plate of this invention makes it possible toproduce visible image thereon with more definition, gloss and fiat thanhave been obtainable when employing a particular resin binder and aclear visible image can be produced by the chargeless electrostaticprinting process.

An organic solvent (e.g. alcohol) mixed with Water, in addition to thecitric acid and water may be added to photoconductive zinc oxide inorder to accomplish the objects of the invention thereby reducing themilling time required to satisfactorily mix all of the ingredients andthe mixture with alcohol can be more easily coated on the base plateregardless of whether the base plate is made of art paper or othersuitable materials.

The following examples will serve to illustrate this invention moreclearly:

3 EXAMPLE III Grams Microcrystalline zinc oxide 1O Citric acid 2 Water 5Ethyl alcohol 20 It will be apparent that the coating mixture of eachexample is applied in a uniform thickness coating to the base therebyproducing electrophotographic plates with the coating being ofsufiicient thickness such as 5,11. to produce a satisfactory image.

The developed images may be made in accordance with electrostaticprinting processes by the use of a charging step, but the charging maybe omitted entirely and the developed image produced in Example II ismore clear than the image produced in Example I and the image producedby Example III is more clear than the image produced by Example II. Theresults show that the developed image becomes clearer as the amount ofcitric acid is increased and the image becomes much clearer by addingorganic solvent. It has also been proved by further experiment that thedeveloped image is Worse as the citric acid is increased above 20% ofthe zinc oxide or the citric acid is decreased to less than 0f the zincoxide.

It will thus be seen that the coating composition applied to a base andthe resulting electrophotographic plate without a particular resinbinder is a simple and and economical product.

The developed image on the electrophotographic plate of the presentinvention has more clarity and definition than has been obtainable withprior art electrophotographic plates and the electrophotographic plateof this invention can be used in chargeless electrostatic printingprocesses thereby simplifying and reducing the cost of office copyingmachines where inexperienced personnel are required to make copies ofgreat clarity.

We claim:

1. An electrophotographic plate capable of use in chargelesselectrostatic printing with or without charging of the plate comprisinga base, a photoconductive coating of zinc oxide, citric acid and waterthereon, the citric acid and zinc oxide having reacted to provide thecoating.

2. A method of making the printing plate of claim 1 comprising addingcitric acid and water to photo-conduc tive zinc oxide producing achemical action between the citric acid and zinc oxide and coating abase plate with said mixture and drying the coating thereon.

3. A method for producing an electrophotographic plate according toclaim 1 comprising adding citric acid, an organic solvent capable ofmixing with water and a small amount of water to photoconductive zincoxide, coating the base plate with the mixture and drying said coating.

4. The invention according to claim 1 in which the zinc oxide and thecitric acid are present in the proportion of 10 parts of zinc oxide toapproximately 1 to 2 parts of citric acid.

5. The invention according to claim 1 in which the photographic plate isfree of other binding materials.

6. The invention according to claim 3 in which the organic solvent isethyl alcohol.

7. The invention according to claim 2 in which the photoconductive zincoxide is microcrystalline and present in an amount of approximately 10parts, the citric acid being present in approximately 1 to 2 parts,water being present in approximately 5 to 25 parts and ethyl alcoholbeing present in approximately 0 to 20 parts.

References Cited UNITED STATES PATENTS 2,993,787 7/1961 Sugarman 96-1WILLIAM L. JARVIS, Primary Examiner US. Cl. X.R.

